We are conducting a large family study of obsessive-compulsive disorder (OCD), conducting thorough psychiatric examinations of 100 OCD probands and their first degree relatives, and 100 control probands and their first-degree relatives. The specific aims of the study are to determine if the rates of OCD, obsessive-compulsive behaviors, tic disorders, and other psychiatric conditions are higher in the relatives of the OCD probands; to compare familial and sporadic (non-familial) OCD probands with respect to clinical features; to clarify the phenotypic spectrum of conditions that may be translated in the OCD families; and to use segregation analysis to investigate the mode of inheritance of OCD. Probands are being randomly selected from five treatment sites. Controls, matched to the OCD cases on age, sex, and race, are being obtained by random digit dialing. We anticipate that the results of the study will indicate that OCD is familial, and we hypothesize that the condition has an underlying genetic basis. Therefore, we are collecting blood samples from members of the OCD families, and extracting DNA and freezing lymphocytes, with the purpose of conducting genetic studies in the future. To date, we have identified 76 OCD and 48 control families who have agreed to participate in the study, and a total of 179 subjects have been examined. Blood samples have been collected from 94 members of the OCD families and are stored in two participating laboratories. We plan to proceed with the protocol so as to include a total of 100 OCD probands and their first-degree relatives. We then will be poised for either a systematic genome-wide search or candidate gene approach to identify the genetic basis of this burdensome neuropsychiatric condition.